At first glance, it looks like a simple piece of plastic or metal: a small, often red, oddly shaped fob meant to dangle from your keyring. However, to the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) and federal prosecutors across the United States, this "keychain" is considered a .

The ATF has repeatedly issued classification letters stating that a drop in auto sear—even one sold as a "keychain," "paperweight," or "display model"—is itself a machinegun if it is shaped and dimensioned to function as a sear.

In the world of firearm accessories and 3D-printed novelties, few items have generated as much legal controversy and law enforcement attention as the so-called "Drop In Auto Sear Keychain."

You do not have to install it. You do not have to own an AR-15. Simply possessing the object, if it is deemed "readily convertible" or designed to fit a firearm, is a federal felony. Conviction carries up to 10 years in prison and a $250,000 fine. The "Intended Use" Trap Proponents of the keychain often argue that adding a keyring hole changes the item's "intended purpose." However, federal courts have consistently rejected this defense. If the object’s geometry matches that of a functional auto sear—critical dimensions like sear surface angle, pin hole spacing, and thickness—the addition of a keyring hole does not provide a legal shield.